Many network applications running on modern digital telecommunications networks rely on accurate time synchronization for correct operation. For example, telecommunication networks may rely on the use of highly accurate primary reference clocks which are distributed network-wide using synchronization links and synchronization supply units. If switches in the networks do not operate with the same clock rates, then throughput may be degraded. File system updates carried out by a number of computers may depend on synchronized clocks. Network security mechanisms may depend on coordinated times across the network. For cellular networks, time synchronization is used to synchronize cell towers to the same clock signal so the cell towers can transmit in predetermined slots without collision.
For time synchronization, typically, independent clocks are synchronized to a clock reference signal. Various protocols and standards may be used for time synchronization. For example, Network Time Protocol (NTP) is a protocol for clock synchronization between computer systems over packet-switched network. NTP may maintain time to within tens of milliseconds over the Internet, and can achieve better accuracy in a local area network. Precision Time Protocol (PTP) is another protocol used to synchronize clocks throughout a computer network. PTP is a more recent protocol and may provide better accuracy than NTP. Global Positioning System (GPS) is also commonly used for time synchronization, but requires a GPS receiver and a line of sight to a GPS satellite.